The present invention relates to a voltage reference generator as is described in the preamble of the first claim.
Such a voltage reference generator is already known in the art, e.g. from the tutorial handbook "Analysis and design of analogue integrated circuits" of Paul R. Gray and Robert G. Meyer, John Wiley and Sons, New-York (1993). Therein on page 344, FIG. 4.49c, a bandgap reference circuit is shown, including an operational amplifier which relates to the operational amplifier means as described in the preamble of the first claim of the present document, associated in a feedback loop to a circuit consisting of the transistors Q1,Q2, and resistors R1,R2 and R3, corresponding to the feedback circuit, as well described in the preamble of the first claim of this document.
Such a configuration, as indicated by this prior art document on the same page, generates at its output terminal a reference voltage, but needs appropriate start-up circuitry in order to insure a stable operation point. The latter condition is of course necessary to ensure that the output voltage is the correct one. However, even in the presence of such a start-up circuit, some transients in the output voltage may occur and the output voltage can have the wrong value. Additional circuits relying on the voltage reference output voltage can thereby malfunction seriously and create erroneous or even hazardous situations. Examples are circuits for accurate analog power-on-reset functions for low supply level conditions, charging circuits for very sensitive Lithium-Ion batteries that need a very precise voltage limitation, circuits for generation of precise supply voltage levels using low drop-out regulators, etc.
At the same time, in applications where this voltage regulator is part of an integrated circuit, the total configuration needs to be as simple as possible because of cost and power consumption issues. This is for instance the case when the aforementioned applications are used in a GSM-chip.